Ah, a Rose by any other...Excuse me, a LimeWire by any other name is Rocket MP3. This Gnutella peer-to-peer files sharing utility is almost identical to its progenitor, the aforementioned LimeWire. Basically, you define a shared folder, search for files, download them and keep them around for others to download to their PCs. It works quite well--there are tons of MP3 files available--however, in my short perusal there were still the numerous malware and ad-ridden downloads that LimeWire suffered.
The MP3 Rocket Web site makes it appear as if you have to pay money for MP3 Rocket; however, you click on the tiny developer link at the bottom of the screen and choose Get Basic, or simply download here for the free version. The $20 pro version removes the nags and ads and promises 25% faster downloads. As long as you're aware that the vast majority of the files you'll find are infringing on copyrights in one way or another, go right ahead--there's still a thriving Gnutella community out there.
Tip: Don't download MP3 files that look undersized, say less than 2MB. It's most likely not the file you want and probably contains an embedded URL that takes you to a Web site, possibly a dangerous one.